1. Field of the Invention
This invention relates to a satellite packet terminal for the communication of packet data through a communication satellite and to a method for transmitting packet data from the same in satellite communication.
2. Description of the Prior Art
In mobile radio communication, the radio zone may be changed along with the movement of a mobile station. When the above communication means is a telephone such as a car telephone or ship telephone, even if the zone switching time is about 1 second, a hit or interruption in communication caused by zone switching does not present a big problem. However, in the case of data communication, missing data caused by a hit at the time of zone switching are fatal. To cope with this problem, in a conventional mobile radio communication system disclosed in Japanese Laid-open Patent Application No. Sho 59-212040, transmission data are temporarily stored in a buffer when the zone is changed and transmitted after the end of a hit. FIG. 4 shows the sequence of a signal flow between a mobile terminal and a network in the above conventional mobile radio communication system. When a zone switch signal is transmitted from a base station 1 (MBS1) to a mobile exchange (AMC) before the processing of zone switching, AMC gives a communication interruption signal 100 to the data processor (CPM) of the mobile terminal. After zone switching from the base station 1 (MBS1) to a base station 2 (MBS2) is completed, the above mobile terminal falls into a hit where it cannot communicate with the base stations (1, 2) until a communication start signal 101 is given from the AMC to the CPM of the above mobile terminal. Then, the above mobile terminal stores data generated from its built-in data terminal in its built-in buffer, takes out the stored data when it receives the communication start signal 101 from the AMC and resumes data transmission.
However, the zone switching system of the mobile communication system which has the above zone system and controls zone switching under the directions of base stations could not be used in satellite communication which has no zone system. For example, when there are buildings, tunnels and trees which interrupt communication between a satellite and a mobile station, communication between a mobile satellite packet terminal and a satellite base station becomes impossible. Even if the satellite packet terminal is not a mobile station but a fixed station, communication with a satellite base station may become impossible due to temporary jamming caused by an airplane or the like. That is, such communication trouble cannot be detected by the satellite base station and reported to the satellite packet terminal. Therefore, when satellite communication between the satellite packet terminal and the satellite base station becomes impossible temporarily, confirmation information on the transmission of the packet data to the satellite is not provided to the data terminal of the satellite packet terminal, and the satellite packet terminal instructs the above data terminal to stop the transmission of the subsequent packet data in accordance with a packet communication protocol (Receive Not Ready). Therefore, smooth data communication is impossible.
It is an object of the present invention which has been made to solve the above problem to provide a satellite packet terminal which enables smooth data communication even when a radio communication channel with a satellite falls into a fault state and a method for transmitting packet data from the same.
According to a first aspect of the present invention, there is provided a method for transmitting packet data from a satellite packet terminal, which comprises the steps of judging whether a radio communication channel is in a fault state or not based on the reception state of a reception signal received from a satellite through the radio communication channel, storing packet data to be transmitted to the satellite in storage means when it is judged that the radio communication channel is in a fault state, and transmitting the packet data stored in the storage means to the satellite sequentially when it is judged that the radio communication channel is recovered from the fault state.
According to a second aspect of the present invention, there is provided a method for transmitting packet data from a satellite packet terminal, which comprises the steps of judging whether a radio communication channel will fall into a fault state based on the change rate of the reception state of a reception signal received from a satellite through the radio communication channel, storing packet data to be transmitted to the satellite in storage means when it is judged that the radio communication channel will fall into a fault state, and transmitting the packet data stored in the storage means to the satellite sequentially when it is judged that the radio communication channel is recovered from the fault state.
According to a third aspect of the present invention, there is provided a satellite packet terminal which comprises a satellite circuit monitoring unit for measuring the reception level of a reception signal received from a satellite through a radio communication channel, a judging unit for judging whether the radio communication channel is in a fault state or not based on the measured reception level, and a prebuffer for storing packet data transmitted from a data terminal, wherein the packet data transmitted from the data terminal housed in the satellite packet terminal are stored in the prebuffer when it is judged that the radio communication channel is in a fault state and transmitted from the prebuffer to the satellite sequentially when it is judged that the radio communication channel is recovered from the fault state.
According to a fourth aspect of the present invention, there is provided a satellite packet terminal, wherein the satellite circuit monitoring unit calculates the change rate of the reception level of the reception signal, the judging unit judges whether the radio communication channel will fall into a fault state based on the change rate of the reception level, and the packet data transmitted from the data terminal are stored in the prebuffer when it is judged that the radio communication channel will fall into a fault state and transmitted from the prebuffer to the satellite sequentially when it is judged that the radio communication channel is recovered from the fault state.
According to a fifth aspect of the present invention, there is provided a satellite packet terminal which comprises a satellite circuit monitoring unit for detecting whether a reception signal received from a satellite through a radio communication channel is synchronized or not, a judging unit for judging whether the radio communication channel is in a fault state or not based on the synchronism of the reception signal, and a prebuffer for storing packet data transmitted from a data terminal, wherein the packet data transmitted from the data terminal housed in the satellite packet terminal are stored in the prebuffer when it is judged that the radio communication channel is in a fault state and transmitted from the prebuffer to the satellite sequentially when it is judged that the radio communication channel is recovered from the fault state.
According to a sixth aspect of the present invention, there is provided a satellite packet terminal, wherein the satellite circuit monitoring unit calculates the frequency of the asynchronism of the reception signal, the judging unit judges whether the radio communication channel will fall into a fault state based on the frequency of the asynchronism of the reception signal, and the packet data transmitted from the data terminal are stored in the prebuffer when it is judged that the radio communication channel will fall into a fault state and transmitted from prebuffer to the satellite sequentially when it is judged that the radio communication channel is recovered from the fault state.
According to a seventh aspect of the present invention, there is provided a satellite packet terminal which comprises a satellite circuit monitoring unit for measuring the C/N ratio of a reception signal received from a satellite through a radio communication channel, a judging unit for judging whether the radio communication channel is in a fault state or not based on the measured C/N ratio, and a prebuffer for storing packet data transmitted from a data terminal housed in the satellite packet terminal, wherein the packet data transmitted from the data terminal are stored in the prebuffer when it is judged that the radio communication channel is in a fault state and transmitted from the prebuffer to the satellite sequentially when it is judged that the radio communication channel is recovered from the fault state.
According to an eighth aspect of the present invention, there is provided a satellite packet terminal, wherein the satellite circuit monitoring unit calculates the change rate of the C/N ratio of the reception signal, the judging unit judges whether the radio communication channel will fall into a fault state based on the change rate of the C/N ratio, and the packet data transmitted from the data terminal are stored in the prebuffer when it is judged that the radio communication channel will fall into a fault state and transmitted from the prebuffer to the satellite sequentially when it is judged that the radio communication channel is recovered from the fault state.
The above and other objectives, features and advantages of the invention will become more apparent from the following description when taken in conjunction with the accompanying drawings.